This invention concerns a bending assembly of a bending machine.
The bending assembly is applied to machines which bend iron products for building work, whether those products are made from bars or rolls, but which advantageously process round, ribbed or shaped bars.
The bending assembly according to the invention is fitted advantageously, but not only, to bending machines of the type disclosed in EP-A-0.501.212.
The bending machines to which this invention is applied are normally used to bend in four directions bundles of bars in which the bars are stacked on each other vertically so as to produce the same geometric configuration from each bar of the bundle, these geometric configurations being used in building work as stirrups for the reinforcement of reinforced concrete.
The bundle of bars is fed in these bending machines until it cooperates with a bending assembly, which is suitably actuated to make the desired bend.
In the following text the word "upstream" means the position upstream of the bending assembly, whereas the word "downstream" means the position downstream of the bending assembly.
In the state of the art the bending assemblies consist of a stationary abutment pin and of a bending pin which rotates about the abutment pin to bend the bundle of bars.
The bending assembly consists of a rotary bending plate on which is located a bending pin substantially perpendicular to the rotary bending plate, the pin being offset from the central axis of rotation of the rotary bending plate.
U.S. Pat. No. 4,049,026 discloses a bending assembly consisting of two stationary abutment elements coupled to define a feed channel along which the bundle of bars to be bent is fed. These abutment elements have their righthand end suitably shaped as a semi-circle, against which the bundle of bars is rested when being bent by a bending pin positioned downstream of the abutment elements and moved by the rotation of the rotary bending plate.
This first form of embodiment enables downstream bends, whether clockwise or anticlockwise, to be made and in particular makes also possible the formation of downstream bends of 180.degree. in most cases.
In some cases, where the bars consist of certain materials, it is impossible to make 180.degree. bends with such types of abutment elements. This embodiment also does not enable any upstream bend to be made.
The above patent discloses another bending machine able to make downstream and upstream bends; in this machine the abutment assembly with which the bar cooperates during the bending step consists of two elements extending lengthwise and facing each other so as to define a stationary feed channel.
But this embodiment does not enable 180.degree. bends to be made inasmuch as it is known that, owing to the resilience of the bars, the bars, if a bend of a given angle has to be made, have to be bent by a greater angle because the bars spring back resiliently after the bending pin has been removed from them.
In this second form of embodiment at least the segment of the bar in contact with the lengthwise surface of the abutment elements is bent by 180.degree. during the bending step but then springs back to define an angle less than 180.degree. when the bending pin is removed.
FR-A-2.177.934 discloses a bending assembly cooperating with stationary abutment means positioned upstream and external to the bending assembly of a rotary type; this bending assembly makes possible only the production of downstream bends, whether clockwise or anticlockwise, but does not make possible the production of upstream bends.
FR-A-1.284.936 discloses a bending assembly in which the working surface includes both upstream and downstream of the bending assembly a plurality of aligned holes with which there cooperate retaining and clamping means that have to be positioned by hand on each occasion according to the diameter of the bars forming the bundle and according to the diameter of the abutment pin.
These operations of positioning by hand the retaining and clamping means make the bending operations long and complicated and thereby reduce considerably the output of the bending machine.
So as to overcome these shortcomings, EP-A-0.501.212 and EP-A-0.502,341 disclose bending machines in which the abutment element consists of a central stationary abutment pin.
To ensure that the part of the bar not bent by the bending pin does not deform but remains straight, this bending machine includes four retaining and clamping means, which can be actuated momentarily and be retracted momentarily. These four retaining and clamping means are arranged in pairs upstream and downstream respectively of the bending assembly; each pair consists of two retaining and clamping means positioned on the opposite sides of the bundle of bars being fed.
To be more exact, these retaining and clamping means have a first working position, in which they protrude from the working surface feeding the bundle of bars and cooperate with that bundle of bars to be bent, and a second retracted inactive position, in which they lie below the working surface.
When a given bend has to be made, the retaining and clamping means cooperating with the end of the bundle of bars opposite to the end to be bent are brought to their working position, whereas the other retaining and clamping means stay in their inactive position.
The inclusion of these retaining and clamping means capable of a movement perpendicular to the surface on which the bundle of bars slides makes the bending machine more complicated and therefore more costly.
Moreover, these movable retaining and clamping means require drive means, such as jacks for instance, which have to be operated automatically according to the bend to be made.
These retaining and clamping means, therefore, entail a plurality of additional elements on the bending machine and have to be operated by the control and governing unit of the bending machine.
Such retaining and clamping means involve higher costs of construction and of management and maintenance of the bending machine.
Furthermore, these retaining and clamping means also require a plurality of specific spare parts, which lead also to greater investments in storage for spares.
EP-A-0.123.231 discloses a bending machine in which the bending assembly comprises an abutment plate which cannot be rotated and a rotary bending plate coaxial with, and external to, the non-rotatable abutment plate.
The abutment plate bears two opposed abutment pins arranged in a plane perpendicular to the plane of feed of the bundle of bars; these two abutment pins define a stationary feed corridor having a constant width defined by the diameter of the abutment pins and by the distance between their centres; in this corridor there passes the bundle of bars to be bent.
During the bending step the bundle of bars is caused to cooperate with one or the other of the abutment pins, depending on whether a clockwise bend or an anticlockwise bend is required.
The bending plate too bears two bending pins arranged along a circumference and positioned at radial positions at a distance apart subtending an angle of about 45.degree. at the centre of the abutment plate.
During the working step the two bending pins too are positioned on opposite sides of the bundle of bars.
Depending on the type of bend, whether clockwise or anticlockwise, to be produced, one or the other of the two bending pins cooperates with the bundle of bars, which rests only against the opposed abutment pin.
In this type of machine at least one of the rolls of the pair of feed rolls, which is positioned immediately upstream of the bending assembly, acts as a second abutment element for the bundle of bars during the bending step.
The abutment pins are positioned opposite and close to each other with a small play additional to the thickness of the bars.
The bending assembly of this type makes possible the production only of downstream bends, that is to say, bends external to the assembly of feed rolls/bending assembly, but does not make possible the production of upstream bends, that is to say, bends at a position between the feed rolls and bending assembly.
Next, it should be borne in mind that during the bending step the feed rolls, which are fitted as cantilevers and act as a second abutment element, undergo heavy stresses which could damage their supporting shafts with resulting problems linked to their operation.